Perspective on Radial-Hydride-Induced Embrittlement

Mike Billone Argonne National Laboratory

DOE-UFD Annual Meeting

UNLV June 7-9, 2016

2

Introduction Background Relevant ranges of peak cladding temperature and stress

Previous Results for High-Exposure Cladding ─ As-irradiated cladding ─ Following cooling from 400oC peak drying-storage temp.

New Data for High-Exposure Cladding ─ As-irradiated condition for Zry-4 ─ Following cooling from 350oC peak drying-storage temp.

FY2016 Tests in Progress

Summary and Perspectives

Outline of Topics

3

Introduction

4

Introduction: Objectives of Argonne Experimental Program

Argonne Experimental Program • Generate data for ductility vs. temperature following slow cooling

from T ≤400°C and decreasing hoop stress (σθ) • Determine ductile-to-brittle transition temperature (DBTT) for each

set of peak drying-storage T and σθ: ductility transition temperature • Characterize extent of radial hydrides and correlate DBTT with

effective length of radial hydrides (RHCF) • From data and stress-strain input, determine failure stresses and

strains for PWR cladding alloys (input into codes) Argonne Collaborations

• EPRI-ESCP Fuels Subcommittee and ORNL: relevant range for σθ • PNNL and ORNL: relevant range for peak cladding temperatures • SNL, PNNL, and ORNL: relevant range of NCT loads and fueled-

cladding response to bending-fatigue loads (experimental)

5

Introduction: Loads on Fuel Rods

Loads on Fuel-Rod Cladding during Drying & Storage • Primarily internal gas-pressure loading (hoop & axial stresses)

Loads on Fuel-Rod Cladding during Transport • Normal conditions of transport (NCT) include vibration and shock

– Axial bending: axial bending stresses (other stresses at pellet-pellet interfaces) – “Pinch” loading at grid spacers: hoop bending stresses

• Hypothetical accident conditions include severe impact loads

F

Internal Pressure pi

Schematic of Pinch-Loading

6

Introduction: Circumferential and Radial Hydrides in High-Exposure PWR Cladding

320 wppm H

As-Irradiated After Cooling from 400oC/110-MPa

76 wppm H

72 wppm H

350 wppm H

ZIRLO™

M5®

7

Introduction: Relevant Ranges of Cladding Temperature & Stress

Cladding Temperature • Peak cladding temperature (PCT)

– Determines maximum hydrogen content in solution and available for precipitation as radial hydrides: 206 wppm @ 400°C, 126 wppm @ 350°C, 77 wppm @ 300°C

– Likely to occur during vacuum drying – 400°C NRC-recommended limit; ≤350°C based on UFD S&T calculations

• “Peak” average gas temperature within fuel rods – Determines peak internal pressure given pressure (RIP) at RT – May vary from 180°C (vacuum/static-He) to 340°C (vertical cask with 0.5-MPa He)

Cladding Hoop Stress • Depends on rod internal/external pressure, ID, and wall thickness • “Reasonable” upper bounds for high-burnup PWR fuel rods

– Standard (UO2/Clad) fuel rods: 60−80 MPa – Integral Fuel Burnable Absorber (IFBA fuel rods (UO2/10B/ZIRLO™):

• Hollow blanket pellets (HBP): 80−120 MPa; solid blanket pellets (SBP): 115−155 MPa

8

Introduction: Dissolution (Heating) and Precipitation (Cooling) Curves

0

50

100

150

200

250

300

350

400

450

0 100 200 300 400 500

Hyd

roge

n C

once

ntra

tion

(wpp

m)

Temperature (°C)

Kammenzind Cd (Zry-4)Kammenzind Cp (Zry-4)Kearns Cd (Zr,Zry-2,Zry-4)

Dissolution

Precipitation

ΔTPD 210 wppm

77 wppm

9

Combined Data and Predictions for Rod Internal Pressure (RIP) @ 25oC

0

1

2

3

4

5

6

7

8

9

10

11

40 45 50 55 60 65 70 75

EOL

PWR

RIP

at 2

5°C

(MPa

)

Rod Average Burnup (GWd/MTU)

Data: Standard RodsFRAPCON: Standard RodsFRAPCON-IFBA-HBPFRAPCON-IFBA-SBP

Data Average + 3-σ

Data Average

10

Summary of Previous Results: Cooling from 400oC

11

Response of M5® Cladding following Cooling from 400oC

Test Matrix for High-Exposure M5® (Zr-1wt.%Nb)

• As-irradiated, 76±5 wppm hydrogen • After cooling from 400°C/90-MPa, 58±15 wppm • After cooling from 400°C/111-MPa, 72±10 wppm • After cooling from 400°C/142-MPa, 94±4 wppm

Results for High-Exposure M5® • As-irradiated: high ductility at T ≥20°C (no cracking up through 1.7 mm disp.)

• 90-MPa, 58±15 wppm: high ductility at T ≥20°C, 37±17% RHCF

• 111-MPa, 72±10 wppm: high ductility at T ≥90°C, 54±20% RHCF

• 142-MPa, 94±6 wppm: mod.-to-high ductility at T ≥90°C, 61±18% RHCF

12

Ductility vs. Test Temperature for High-Exposure M5®

0

2

4

6

8

10

12

14

0 25 50 75 100 125 150 175 200 225

Offs

et S

trai

n (%

)

RCT Temperature (°C)

76±5 wppm H58±15 wppm H (90 MPa)72±10 wppm H (111 MPa)94±6 wppm H (142 MPa)

142 MPa at 400°C

111 MPa at 400°C

Ductile

Brittle

High-Burnup M5®

As-Irradiated

90 MPa at 400°C

13

Radial Hydrides in High-Exposure M5® following Cooling from 400oC

111 MPa 72±10 wppm

82 MPa at 228oC 54±20% RHCF

90 MPa 58±15 wppm

65 MPa at 210oC 37±17% RHCF

142 MPa

94±6 wppm 110 MPa at 251oC 61±18% RHCF

14

Assessment of M5® Database following Cooling from 400oC

Need Data for 90−110 MPa with 75−95 wppm Hydrogen

• Ductility improved with decrease in both hydrogen and hoop stress • Note: licensing issue; PCT ≤350°C, Peak σθ <80 MPa • Low H-content and low σθ → no radial hydride issue

Need End-of-Life (EOL) RIP Data for M5®-clad fuel rods • No available data • ≤9 new data points planned for “sister” rod characterization

Need Tests at <400°C • Less annealing would occur at lower peak temperatures • Need to confirm previous results at T ≤350°C

15

Response of Zry-4 Cladding following Cooling from 400oC

Test Matrix for High-Exposure Zircaloy-4 • As-Irradiated, 300±15, 616±78, 640±140 wppm hydrogen • After cooling from 400°C/113-MPa, 520±90 wppm hydrogen • After cooling from 400°C/145-MPa, 615±82 wppm hydrogen

Results for High-Exposure Zircaloy-4 • As-irradiated

– 300±15 wppm: high ductility at 20°C (no cracking to 1.7 mm displace.) – 640±140 wppm (>850 wppm local): no-to-low ductility at ≤90°C (brittle?) – 616±78 wppm: refined test method, ductility = 2.6±0.7% vs. 1% limit

• 113 MPa, 520±90 wppm: low ductility at 20°C, 9±5% RHCF – Recommended test at 350°C/110-MPa (4 RCT data points at 20°C)

• 145 MPa, 615±82 wppm: low ductility at 90°C, 16±4% RHCF

16

Ductility vs. Test Temperature for High-Exposure Zircaloy-4

0

2

4

6

8

10

12

14

0 25 50 75 100 125 150 175 200 225

Offs

et S

trai

n (%

)

RCT Temperature (°C)

300±15 wppm H640±140 wppm H520±90 wppm H615±82 wppm H

Brittle

Ductile

145 MPa at 400°C

113 MPa at 400°C

High-Burnup Zircaloy-4

As-Irradiated

17

Ductility vs. Test Temperature for As-Irradiated, High-Exposure Zry-4

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100 120 140 160

Perm

anen

t Str

ain

(%)

RCT Temperature (°C)

300±15 wppm H

640±140 wppm H

616±78 wppm H

Ductile

As-Irradiated High-Burnup

Zircaloy-4

18

Crack Depth vs. Load Drop for As-Irradiated Zry-4: Load-Interrupt Tests

44% Wall Crack 27% Load Drop 2.1% “Ductility”

41% Wall Crack 22% Load Drop 2.2% “Ductility”

39% Wall Crack 24% Load Drop 2.7% “Ductility”

19

Response of ZIRLO™ Cladding following Cooling from 400oC

Test Matrix for High-Exposure ZIRLO™ (Zr-1wt.%Nb-1wt.%Sn)

• As-Irradiated, 530±70 wppm hydrogen • After cooling from 400°C/80-MPa, 535±50 wppm hydrogen • After cooling from 400°C/89-MPa, 530±115 wppm hydrogen • After 3-cycle cooling from 400°C/88-MPa, 480±131 wppm hydrogen • After cooling from 400°C/111-MPa, 385±80 wppm hydrogen (2 tests) • After cooling from 400°C/141-MPa, 650±190 wppm hydrogen

Results for High-Exposure ZIRLO™

• As-irradiated, 530±70 wppm: mod.-to-high ductility at T ≥20°C • 80 MPa, 535±50 wppm: mod-to-high ductility at T ≥20°C, 9±3% RHCF • 89 MPa, 530±115 wppm: low ductility at 23°C, 19±9% RHCF • 88 MPa, 480±131 wppm: low ductility at 23°C, 20±9% RHCF (3-cycle cool.) • 111 MPa, 350±80 wppm: high ductility at 150°C, 32±13% RHCF • 141 MPa, 650±190 wppm: brittle at 150°C, mod. ductility at 195°C

20

Ductility vs. Test Temperature for High-Exposure ZIRLO™

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140 160 180

Offs

et S

trai

n (%

)

RCT Temperature (°C)

530±70 wppm H

535±50 wppm H

530±115 wppm H

480±131 wppm H

385±80 wppm H

Brittle

Ductile

111 MPa at 400°C

80 MPa at 400°C

High-Burnup ZIRLO™ As-Irradiated

89 MPa at 400°C

21

Radial Hydrides in High-Exposure ZIRLO™ following Cooling from 400oC

141 MPa (128 MPa @ Tp)

650 wppm

111 MPa (101 MPa @ Tp)

350 wppm

80 MPa (72 MPa @ Tp)

535 wppm

89 MPa (80 MPa @ Tp)

530 wppm

22

Response of ZIRLO™ Cladding following Cooling from 400oC

Assessment of Database for High-Exposure ZIRLO™ • Need data in peak stress range of 90−110 MPa prior to cooling

– DBTT increased by 100°C within this stress range – Stress range relevant to WEC-IFBA rods

• Need repeat tests to determine DBTT with more precision – Standard-fuel ZIRLO™ rods: 60−80 MPa relevant peak stress range

• Radial hydride embrittlement not anticipated

– ZIRLO™-clad fuel pellets with ZrB2 (enriched in 10B) coating Integral Fuel Burnable Absorber (IFBA) rods Relevant stress ranges: 80−120 MPa and 115-155 MPa for 2 designs

• Need tests at <400°C to determine net effects on DBTT of reduction in annealing and reduction in dissolved hydrogen available for precipitation

23

New Data for 350oC Peak Drying-Storage Temperature

24

High-Exposure ZIRLO™ and M5® following Cooling from 350oC

Expectations • ZIRLO™

– Decrease (80 wppm) in dissolved hydrogen and in precipitation temperature – Decrease in internal pressure and hoop stress at precipitation initiation – Possible decrease in annealing of irradiation hardening (lower ductility matrix) – Anticipated net effect: decrease in DBTT

• M5® – No change in dissolved hydrogen, precipitation temperature, precipitation stress – Possible decrease in annealing of irradiation hardening (lower ductility matrix) – Anticipated net effect: no change in DBTT

ZIRLO™ Tests at 350°C • 94 MPa (84 MPa @ Tp), 644±172 wppm, 1-cycle cooling

– Long radial hydrides (37±11%), low ductility @ ≤135°C, mod. ductility @ 150°C • 93 MPa (83 MPa @ Tp), 564±177 wppm, 3-cycle cooling

– Long radial hydrides (30±11%), low ductility @ ≤120°C, high ductility @ ≥135°C • No effects of cycling, but DBTT comparable to DBTT for 400°C/111-MPa

25

Ductility Data for High-Exposure ZIRLO™ following Cooling from 350oC

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140 160

Offs

et S

trai

n (%

)

RCT Temperature (°C)

400°C/89-MPa, 530±115 wppm, 1C400°C/88-MPa, 480±131 wppm, 3C350°C/93-MPa, 564±177 wppm, 3C350°C/94-MPa, 644±172 wppm, 1C400°/111-MPa, 350±80 wppm, 1C400°/111-MPa, 425±63 wppm, 1C

Brittle

Ductile

High-Burnup ZIRLO™

26

Radial Hydrides in ZIRLO™ for 1- and 3-Cycle Drying Tests following cooling from 350oC

1-Cycle-350oC Test 94 MPa → 84 MPa

37±11% RHCF ≥50% Max. RHCF

3-Cycle-350oC Test 93 MPa → 83 MPa

30±11% RHCF ≥50% Max. RHCF

27

FY2016 Tests in Progress

ZIRLO™ following Cooling from 350°C • 90-MPa (1-cycle) test with lower-H (350 wppm) and 24-h hold time

– High-hydrogen content (644±172 wppm) may have degraded cladding – 350 wppm is closer to expected hydrogen content at ≤55 GWd/MTU – Compare results to 400°C/111-MPa test with 350 wppm & 24-h hold – Use load-interrupt method to improve data analysis and reduce scatter – If ductility values are still low, investigate effects of annealing

M5® following Cooling from 350°C • 90-MPa target hoop stress, 75−95 wppm target H-content

– Radial hydride treatment (RHT) completed – Metallography: oxide and metal wall thicknesses, 50±14% RHCF – 89-MPa actual hoop stress – Hydrogen content: 80±7 wppm; hydrides not continuous in axial

direction; ring compression tests in progress

28

ANL Perspective

DBTT or Ductility Transition Temperature • Not a material property like Young’s modulus • Depends on orientation/length of hydrides and orientation of loads • Transport at T <DBTT does not imply failure • ANL data may be used to determine hoop failure stresses/strains

Relevant Hoop Stresses during Drying and Storage • Depend on end-of-life internal gas pressures

– Standard rods have lower gas pressures (He-fill + fission gas) – IFBA rods have higher gas pressures (He-fill + He from B-10 + fission gas)

• Depend on average gas temperature during drying/storage – Horizontal/He < vertical/vacuum < vertical/He < vertical/convective-He

• “Reasonable” upper-bound hoop stresses – Standard PWR rods: 60−80 MPa – ZIRLO™-clad IFBA rods with annular blanket pellets: 80−120 MPa – ZIRLO™-clad IFBA rods with solid blanket pellets: 115−155 MPa

29

Relevant Publications

M.C. Billone et al. Phase I Ring Compression Testing of High-Burnup Cladding. FCRD-

USED-2012-000039, Dec. 21, 2011. M.C. Billone et al. Baseline Studies for Ring Compression Testing of High-Burnup

Fuel Cladding. FCRD-USED-2013-000040, ANL-12/58, Nov. 23, 2012. M.C. Billone et al. “Ductile-to-brittle transition temperature for high-burnup cladding

alloys exposed to simulated drying-storage conditions,” J. Nucl. Mater. 433 (2013) 431-448.

M.C. Billone et al., “Effects Drying and Storage on High-Burnup Cladding Ductility,” Proc. IHLRWM Conf., Albuquerque, NM, Apr. 28 – May 2, 2013.

M.C. Billone et al., “Baseline Properties and DBTT of High-Burnup PWR Fuel Cladding Alloys,” PATRAM-2013, San Francisco, CA, Aug. 18-23, 2013.

M.C. Billone et al. Embrittlement and DBTT of High-Burnup PWR Fuel Cladding Alloys. FCRD-UFD-2013-000401, ANL-13/16, Sept. 30, 2013.

M.C. Billone et al. Effects of Multiple Drying Cycles on High-Burnup PWR Cladding Alloys. FCRD-UFD-2014-000052, ANL-14/11, Sept. 26, 2014.

M.C. Billone et al., “Characterization and Effects of Hydrides in High-Burnup PWR Cladding Alloys,” Proc. IHLRWM Conf., Charleston, SC, Apr. 12–16, 2015.

M.C. Billone et al., Effects of Lower Drying-Storage Temperatures on the DBTT of High-Burnup PWR Cladding. FCRD-UFD-2015-000008, ANL-15/21, Aug. 28, 2015.

30

Acknowledgment

This work is supported by the Used Fuel Disposition Research and Development, Office of Nuclear Energy (NE-53) under Contract DE-AC02-06CH11357.

Mike Billone Manager, Irradiation Performance Nuclear Engineering Division Argonne National Laboratory 9700 S. Cass Ave., Bldg. 212 Argonne, IL 60439 630-252-7146 billone@anl.gov

31

Backup Slides

32

“Reasonable” Upper-Bound Hoop Stresses for Standard PWR Rods

50

60

70

80

90

100

160 180 200 220 240 260 280 300 320 340 360

PWR

Rod

Hoo

p St

ress

(MPa

)

Gas Temperature (°C)

10-Micron Oxide40-Micron Oxide80-Micron Oxide

33

“Reasonable” Upper-Bound Hoop Stresses for Standard PWR Rods

80

90

100

110

120

130

140

150

160

160 180 200 220 240 260 280 300 320 340 360

PWR

Rod

Hoo

p St

ress

(MPa

)

Gas Temperature (°C)

IFBA-HBPIFBA-SBP

34

RHT Experimental Method for 1- and 3-Cycle Drying of Pressurized Rodlet

Rodlet Fabrication 175

200

225

250

275

300

325

350

375

400

425

0 10 20 30 40 50 60 70 80 90

Tem

pera

ture

(°C

)

Time (hours)

Peak T ≤206 wppm H

in solution

Precipitation T

5°C/h

Δp = Δp(T) σθ = σθ(T) 1-Cycle

Drying

35

Temperature Histories for 1- and 3-Cycle Tests at 350oC Peak RHT Temperature

175

200

225

250

275

300

325

350

375

0 10 20 30 40 50 60 70 80

Tem

pera

ture

(°C

)

Time (Hours)

4.8°C/h

126-wppm H in solution

Precipitation Temperature

(285°C)

1 Cycle

36

Ring Compression Test (RCT)

Applied load @ 12 o’clock

Ductility: permanent (dp/Dmo) or offset strain (δp/Dmo) prior to >50% wall crack

Embrittlement: dp/Dmo <1% or δp/Dmo <2%

Controlled displacement rates 5 mm/s typical

1.7-mm maximum displacement

Controlled temperature

Maximum δp/Dmo ≈10% for 1.7 mm displacement

37

RCT Benchmark Test with As-Fabricated M5®

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(P in

kN

)

Displacement (δ in mm)

KLM = 1.06 kN/mm

Offset Displacement = 0.94 mm Permanent Displacement = 0.83 mm

KLC = 1.23 kN/mm 0.94 mm

KUM = 0.81 kN/mm

0.83 mm

38

RCT Benchmark Tests with As-Fabricated and High-Exposure M5®

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Unl

oadi

ng/L

oadi

ng S

tiffn

ess

Rat

io

Offset Strain (%)

As-Fabricated Cladding

High-Burnup Cladding

39

Load-Displacement Curve and Crack at ≈6 O’Clock for 3-Cycle Rodlet Tested at 135oC RCT

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kN

)

Displacement (mm)

Ring 105E3 at 135°C 564±177 wppm H 30±11% RHCF 11.9% Offset Strain

KLM = 0.90 kN/mm

478 N 423 N

1.12 mm

KU = 0.70 kN/mm

40

Load-Displacement Curves for 1-Cycle Rodlet Tested at 135oC RCT

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kN

)

Displacement (mm)

Ring 105F3 at 135°C 644±172 wppm H 37±11% RHCF 1.1% Offset Strain

KLM = 0.90 kN/mm

449 N

43%

0.10 mm

KU = 0.88 kN/mm

41

Load-Displacement Curve and Crack at 12 O’Clock for 1-Cycle Rodlet Tested at 150oC RCT

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kN

)

Displacement (mm)

Ring 105F7 at 150°C 644±172 wppm H 37±11% RHCF 2.9% Offset Strain

KLM = 0.86 kN/mm

322 N

281 N

25%

0.27 mm

KU = 0.79 kN/mm

42

Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa

Maximum – 95% RHCF

43

Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa; after Grinding off 0.5 mm & Polishing

Maximum – 95% RHCF

44

Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa; after Grinding off ≈0.1 mm & Polishing

Maximum – 91% RHCF